Fiberoptic temperature/pressure sensor system

ABSTRACT

A fiberoptic sensing system comprising a light source, a sensor responsive to external stimulus, an optical fiber connected to the light source and the sensor, a detector arranged to receive light from the optical fiber, and output electronics electrically connected to the detector. The sensor includes a reflective surface arranged so as to reflect light from the optical fiber. This reflective surface is movable relative to the optical fiber. The light source comprises a light-emitting diode and a reference diode electrically connected to the source of electrical energy and to the light-emitting diode. A beamsplitter is disposed about the light source, the optical fiber, and the photodetector. The detector includes a transimpedance amplifier and a RMS to DC converter. The output electronics includes a gain control and a offset control. The sensor may be either a temperature sensor or a pressure sensor.

TECHNICAL FIELD

The present invention relates to instrumentation for detectingtemperature and pressure. More particularly, the present inventionrelates to fiberoptic techniques for monitoring temperature and pressureconditions in a remote location.

BACKGROUND ART

Fiberoptics is the branch of physics concerned with the propagation oflight that enters a thread or rod of transparent material at one end andis totally reflected back inward from the wall, thereby beingtransmitted within the fiber from one end to the other. Fiberoptics iswidely applied in medical practice to observe the human body internally.Fiberoptic fibers have also been used to transmit light signals carryinginformation from both electronic and optical sensors.

The accurate measurement of temperature is important in many chemicalprocesses to avoid harm to materials and equipment resulting fromtemperatures outside a specified range. Its determination is alsonecessary in situations in which it is a needed variable in thecomputation of properties, such as pressure, viscosity, or density.Methods of sensing temperatures depend upon the measurement of thechanges caused by temperature. Many devices, such as the familiarglass-stem thermometer, measure the change in volume of a substance,such as mercury, caused by a change in temperature. Thermistors aredevices that measure temperature by the change it causes in theirelectrical resistance. Temperature may be inferred by measuring theintensity of the total radiation emitted, as radiation pyrometers do, orby observing changes in color or shape of certain materials. Thesedevices exist in such multiplicity to meet differing requirements ofsize, accuracy, range, and ability to withstand the testing environment.

One of the most versatile and widely used of these devices is thethermocouple. It operates on the principle that heat imparted to thejunction of two different metals or alloys causes a voltage that varieswith the amount of heat applied. The device consists of two wires ofdifferent metal, fused together at one end to form a measuring junction.The free ends are connected to a measuring instrument, which convertsthe voltage at the thermocouple junction into a measurement of thetemperature, the two quantities being directly proportional.

Pressure, like temperature, is a variable that must be measuredaccurately in industry, particularly in the chemical industry.Determination of pressure is vital, for instance, in the control ofhydrogenation (addition of hydrogen) and distillation in petroleumprocessing. Again, like temperature, pressure is a variable needed inthe calculation of other properties. Pressure-measuring devices varywith the range over which they are meant to be used. In the vacuumrange, gas pressure is detected by measuring the current generated dueto ionization of the gas or by measuring the thermal conductivity of therarified gas. Pressures in this region are also calculated bycompressing a known volume of the gas until it reaches a fixed pressure.When the new volume is measured, the original pressure can be computedby use of Boyle's Law, which states that the product of the originalvolume and original pressure is equal to the product of the new volumeand new pressure.

In the atmospheric pressure range and above, elastic pressure elementsare widely used; they measure the expansion caused by pressure. Whilesome devices measure the expansion of a diaphragm or a bellows, the mostcommonly used industrial sensor is the so-called Bourdon tube consistingof a tube in the form of a 250° arc. The process pressure is connectedto the fixed socket end of the tube, while the tip end is sealed andconnected via a series of links and gears to a pointer. Because of thedifference between its inside and outside radii, the Bourdon tube tendsto straighten when pressure is applied. The resulting motion of thesealed tip is a function of this pressure, and thus, the position of thepointer yields a measure of the process pressure.

A device that has many applications in this pressure range is the straingauge, which is based upon the fact that metallic conductors subjectedto strain exhibited corresponding change in electrical resistance. Thereare many types of strain gauge, but all are constructed so that theprocess pressure causes a strain, and thus a change in electricalresistance, which is measured for a visual display. In one example, theprocess pressure is applied to a flat diaphragm. The strains resultingfrom the diaphragm deflection cause changes in the resistance of fourstrain elements bonded directly to the underside of the diaphragm. Thischange in resistance is measured as an indication of process pressure.

In many circumstances, particularly in the dangerous environment ofchemical processing industries, it is necessary to measure pressure andtemperature while avoiding any potential ignition of volatile gases inthe area. Whenever electricity is directly applied in the measurement oftemperature and pressure in such applications, there is an inherent riskthat a short circuit or other electrical malfunction may occur thatcould ignite a dangerous mixture.

While fiberoptics have been used in the past for the measurement oftemperature and pressure, these techniques have required the use ofcomplicated bundles of optical fibers and electronics associated withthose optical fibers. These arrangements have been costly, logisticallydifficult, unduly complicated, and generally unreliable. The presentinvention is believed to be the first application of a single opticalfiber approach to the measurement of temperature and pressure.

It is an object of the present invention to provide an inherently safetechnique for the measurement of temperature and pressure.

It is another object of the present invention to provide a fiberopticsensor system that produces an analog output relative to the effect oftemperature or pressure upon a sensor.

It is still another object of the present invention to provide afiberoptic sensing system that stabilizes the source of light that isdirected toward the optical fiber within such a system.

It is still another object of the present invention to provide afiberoptic sensing system for the measurement of temperature or pressurethat utilizes a single optical fiber for the transmission of lightinformation to and from the sensing device.

These and other objects and advantages of the present invention willbecome apparent from a reading of the attached specification andappended claims.

DISCLOSURE OF THE INVENTION

The present invention is a fiberoptic sensing system comprising a lightsource; a sensor responsive to an external stimulus; an optical fiberfor transmitting light from the light source to the sensor; aphotodetector arranged so as to receive light from the optical fiber;and output circuitry electrically connected to the photodetector. Inthis invention, the sensor includes a reflective surface for reflectinglight from the optical fiber. This reflective surface is movablerelative to the optical fiber in response to the external stimulus. Thephotodetector is responsive to the power of light emitted by the opticalfiber. The output circuitry produces a signal relative to the light asreceived by the photodetector.

The light source of the present invention comprises a light-emittingdiode, and a reference diode electrically connected to the source ofelectrical energy for the light-emitting diode and to the light-emittingdiode. This reference diode serves to stabilize current acting upon thelight-emitting diode. The reference diode is made up of a Zener diodecircuit, an operational amplifier electrically connected to the Zenerdiode, and a potentiometer electrically connected to the Zener diode,the operation amplifier, and the light-emitting diode. The potentiometeris used for setting the power level to the light-emitting diode.

In one embodiment, the sensor is a temperature sensor. This temperaturesensor comprises a housing, a carrier arranged within the housing, andat least one bimetallic strip connected to the carrier at one end andanchored to the housing at the other end. The bimetallic strip allowsthe carrier to move longitudinally within the housing in response tochanges in temperature affecting the bimetallic strip. The carrier has areflective surface affixed thereto. This temperature sensor also has asuitable fiberoptic connector arranged about one end of the housing suchthat the optical fiber is positioned in parallel relationship to thereflective surface on the carrier.

In the other embodiment, the sensor of the present invention is apressure sensor. This pressure sensor comprises a body, a carrierelement arranged within the body, and a pressure-responsive memberconnected to the carrier element. The carrier element of the presentinvention has a reflective surface affixed thereto. Thepressure-responsive member is movable within the body in response topressure acting on the member. The pressure-responsive member is apiston disposed within a cylindrical cavity of the body. The piston isarranged to move longitudinally within the body in response to pressureacting on the piston. The pressure sensor of the present inventionfurther includes a Belleville spring disposed within the body andjuxtaposed against one end of the piston. This Belleville spring exertsa desired amount of resistance against the longitudinal movement of thepiston. As with the temperature sensor, the pressure sensor of thepresent invention has a suitable fiberoptic connector such that theoptical fiber can be positioned in parallel relationship to thereflective surface.

The optical fiber of the present invention comprises a single opticalpathway from the light source to the sensor. This includes abeamsplitter disposed generally about the light source, one end of theoptical fiber, and the photodetector. The beamsplitter passes light fromthe light source to the optical fiber and passes light from the opticalfiber to the photodetector.

The photodetector is positioned relative to the optical fiber so as tobe electrically responsive to light emitted by the optical fiber forproducing a current relative to the power of the light from the opticalfiber. This photodetector further comprises a transconductance amplifierelectrically connected to the photodetector for converting the currentfrom the photodetector into a voltage, and a RMS to DC converterelectrically connected to the transconductance amplifier for producing adirect current signal proportional to the voltage.

The output circuitry of the present invention includes a gain controlelectrically connected to the photodetector for providing a full scalesetting with respect to the signal produced by the photodetector. Theoutput circuitry also includes suitable offset control circuitry that iselectrically connected to the photodetector for providing an adjustablezero setting with respect to the signal produced by the photodetector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical representation of the fiberoptictemperature/pressure sensor system in accordance with the presentinvention.

FIG. 2 is a cross-sectional view in side elevation of the pressuresensor in accordance with the present invention.

FIG. 3 is a cross-sectional view in side elevation of the temperaturesensor in accordance with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, there is shown at 10 the fiberoptictemperature/pressure sensor system in accordance with the presentinvention. The fiberoptic temperature/pressure sensor system 10comprises a light source 12, sensor means 14, fiberoptics 16, detectioncircuitry 18, and output circuitry 20.

The light source 12 of the present invention offers a stabilizedapproach to the introduction of light into the fiberoptics. Light source12 is powered by a voltage source 22. In order to offer the most stablelight source, the light source 12 comprises semi-precision currentsource 24, reference (Zener) diode 26, potentiometer 28, operationalamplifier 30, and light-emitting diode 32. The semi-precision currentsource 24 is a well-known, off-the-shelf component. The reference diode26 employs a Zener diode and has a temperature compensation circuitbuilt in. This means that the temperature drift of the reference diode26 is almost zero. The potentiometer 28 is included within light source12 so as to vary the power emitted by the light-emitting diode 32. Inkeeping with the proper design of this light source so as to achievemaximum stability, the potentiometer should have a very low temperaturecoefficient. The operational amplifier 30 is incorporated into thisdesign so as to stabilize the voltage across the resistor. Also, sincethe op-amp 30 is enclosed around the transistor, the temperature driftabout the transistor is zero since it is compensated by the op-amp 30.In addition, resistors 36 and 38 should be selected so as to have a zerotemperature coefficient. Each of these elements interact within lightsource 12 so as to produce an extremely stable current acting on LED 32.The stability of the light from LED 32 is a critical design factor ofthe present invention. The stability of the light from LED 32 allows therest of the system to properly make an analog measurement of thetemperature/pressure characteristics sensed by sensor 14. In addition,such light stability enhances the accuracy and repeatability of themeasurements of the present invention.

Sensor 14 may be either a pressure sensor (as seen in FIG. 2) or atemperature sensor (as illustrated in FIG. 3). The major requirement ofsensor 14 is that it includes a reflective surface for reflecting lightfrom the fiberoptics 16. This reflective surface should be movable inresponse to an external stimulus, such as a change of temperature orpressure. In this manner, the light emitted by light-emitting diode 32into fiberoptics 16 may be reflected back into the fiberoptics. A morecomplete description of the temperature and pressure sensors that makeup sensor 14 will be provided hereinafter.

Fiberoptics 16 is a single optical path extending from beamsplitter 40to sensor 14. Optical fiber 16 is a type of transmission media thatallows light to be transmitted long distances and around corners withlittle loss without interference from other light sources. Optical fiber16 is a very thin tube of quartz, glass, or plastic which is designed totransmit a beam of light from one end to the other by essentiallyreflecting it from side to side as it travels down the fiber. Inaccordance with the present invention, fiberoptics 16 comprise a singleoptical fiber pathway. One end of fiberoptics 16 is coupled tobeamsplitter 40 and arranged so as to receive light from LED 32. Thelight from LED 32 will travel along optical fiber 16 to its other endwithin sensor 14. Optical fiber 16 may have a length as long as severalkilometers. This maximizes the distance between the electrical circuitryof the present invention and the potentially hazardous environment ofsensor 14.

Beamsplitter 40 includes a housing that contains the beamsplitter andreceives the LED 32, the optical fiber 16, and the detector components18 of the present invention. Specifically, beamsplitter 40 is an opticalarrangement that reflects part of the beam of light and transmits partof that beam of light. The fiberoptics 16 are arranged such that theoptical fiber receives the light as transmitted by LED 32. Photodetector42 is also connected to beamsplitter 40. In the preferred embodiment ofthis invention, these components are arranged such that light will betransmissive therebetween. In other words, light from LED 32 should passto the beamsplitter 40 and be received by fiberoptics 16. The lightreturning through fiberoptics 16 from sensor 14 is reflected offbeamsplitter 40 and is received by photodetector 42.

Detector circuitry 18 is comprised of photodetector 42, transconductanceamplifier 44, voltage amplifier 46, RMS to DC converter 48, and low passfilter 50. Photodetector 42 receives the light transmitted from sensor14 by fiberoptics 16. Photodetector 42 converts this light input into anelectrical output. In this arrangement, photodetector 42 transmits an ACsignal to transconductance amplifier 44. Transconductance amplifier 44is electrically connected to photodetector 42 and converts the currentfrom photodetector 42 into a voltage. This voltage is a function of thepower of light received by photodetector 42. In this manner, as morelight is reflected by sensor 14 into optical fiber 16, the greateramount of voltage will be transmitted by the transconductance amplifier44. Voltage amplifier 46 is electrically connected to transconductanceamplifier 44. Voltage amplifier 46 elevates the voltage produced by thetransconductance amplifier 44 into a level that is suitable for workingwith. RMS to DC converter 48 converts the signal from voltage amplifier46 into a DC signal proportional to the pwoer of light that hitphotodetector 42. As used in the present invention, this DC converterproduces an observable indication of the level of power strikingphotodetector 42. As such, this allows the present invention to make anaccurate analog measurement of temperature, pressure, or any otheranalog quantity. The use of this circuit becomes possible under thepresent invention because of the stability of the light source 12, asdescribed hereinbefore. Low pass filter 50 receives the signal from RMSto DC converter 48 and removes electrical disturbances that are not partof the desired signal from photodetector 42.

The output circuitry 20 of the present invention comprises gainadjustment circuitry 52 and offset circuitry 52. Gain circuitry 52provides a full scale setting relative to the signal produced by thedetector circuitry 18. The offset circuitry 54 gives an adjustable zerosetting and span with respect to the signal of the detection circuitry18. Gain circuitry 52 and offset circuitry 54 are electrically connectedtogether and pass an output that may be transferred to instrumentationexternal of the present system. This instrumentation could produce ahumanly perceivable readout of the quantity that is being measured bysensor 14. For example, the output of the present invention could betransmitted to a computer external of the system. The computer couldmonitor the quantity being measured by sensor 14.

FIG. 2 shows the pressure sensor 60 in accordance with the presentinvention. Pressure sensor 60 comprises body 62, carrier element 64, andpressure responsive member 66. Carrier element 64 is integrally affixedto pressure responsive member 66. A reflective surface 68 is affixed tothe top of carrier element 64.

Body 62 has a male threaded section 70 at its lower end. Threadedsection 70 allows pressure sensor 60 to be inserted into a pipeline ortank, or other area desired to be measured. A shoulder 72 extends fromthe top portion of this threaded area 70. Body 62 has a generallycylindrical outer surface 74 located generally above threaded section70. Body 62 also includes a support member 76 that is affixed to theinterior of body 62 by bolt 78. Bolt 78 is connected to the interior ofcylindrical section 74 in a threaded arrangement. Support member 76 ismaintained in proper position by the proper tightening of bolt 78 withinthe interior of threaded section of the body 62. Support member 76 has agenerally cylindrical internal cavity 80 that receives the carrierelement 64 and reflective surface 68. Support member 76 has a threadedupper section 82. Threaded section 82 receives fiberoptic couplingelement 84.

Fiberoptic coupling 84, along with fiberoptics 16, is inserted into theinterior cavity 80 of support member 76 such that the optical fiber 16has its light-emitting end maintained in a generally face-to-facerelationship with reflective surface 68.

Carrier element 64 is generally cylindrical in configuration and fitswithin the interior cavity 80 of support element 76. Carrier element 64is arranged so as to move longitudinally within the interior cavity 80.The movement of carrier element 64 is initiated and maintained by themovement of pressure responsive member 66.

Pressure responsive member 66 is a piston that is fitted into thecylindrical cavity 86 corresponding to threaded section 70 of body 62.Piston 66 has a generally cylindrical surface that fits withincylindrical cavity 86. Piston 66 is maintained within cylindrical cavity86 in a fluid-tight arrangement through the use of O-rings 88 that areinserted into grooves about piston 66. At its upper end, piston 66 has acylindrical section 90 of greater diameter than the main portion ofpiston 66. This greater diameter portion 90 is designed so as to fitagainst shoulders 92 formed within the interior of body 62. Carrierelement 64 is affixed to, or integrated into, the top of greaterdiameter section 90. In this arrangement, any movement of piston 66 willresult in a corresponding movement of carrier element 64 and reflectivesurface 68. A Belleville spring 94 is disposed between the bottom end ofsupport member 76 and the top of greater diameter section 90 of piston66. Carrier element 64 passes through the opening on the interior ofBelleville spring 94. Belleville spring 94 is disposed in such aposition so as to offer a desired amount of resistance to the movementof piston 66 within cavity 86. The amount of resistance of Bellevillespring 94 can be changed by varying the thickness, the material, or theangle of inclination of the sides of the spring.

As used, pressure sensor 60 will change the intensity of the lightreflected by reflective surface 68 in correspondence to the movement ofpiston 66. This change in reflectance (and power of light reflected)will correspond and correlate with the pressure acting on pressureresponsive member 66.

FIG. 3 shows the temperature sensor 100 in accordance with the preferredembodiment of the present invention. Temperature sensor 100 comprises ahousing 102, a carrier 104, and heat responsive members 106. Housing 102is a generally cylindrical member having a generally cylindricalinternal cavity 108. At its upper end, housing 102 includes a fiberopticconnector 110. Fiberoptic connector 110 is of the type to receive oneend of the optical fiber 16. This connector is designed to position theoptical fiber 16 such that the end of the optical fiber 16 is inface-to-face relationship with the reflective surface 112 affixed tocarrier 104. At its lower end, housing 102 includes an anchor portion114. Anchor portion 114 has a bore extending therethrough and transverseto the longitudinal axis of housing 102. This bore is of the type toreceive suitable screws, threaded bolts, or other types of connectionarrangements.

Carrier 104 has a generally cylindrical section 116. On top of thiscylindrical section 116 is the reflective surface 112. Reflectivesurface 112 may be integrated onto, affixed to, or otherwise attached tocylindrical section 116 of carrier 104. Carrier 103 also has anattachment section 118 extending beneath cylindrical section 116.Attachment section 118 also has a suitable bore extending therethroughfor receiving an end of temperature sensitive member 106. As used withinthe concept of the present invention, carrier 104 is capable of freemovement within internal cavity 108 of housing 102.

Temperature sensitive member 106 comprises a pair of bimetallic strips120 and 122. Each of these bimetallic strips is comprised of an innerstrip 124 and an outer strip 126. The inner strip 124 and the outerstrip 126 are affixed to each other in face-to-face relationship. Theinner strip 124 has a higher coefficient of expansion than outer strip126. One end of bimetallic strips 120 and 122 is affixed to anchor 114by pins 128. The other end of bimetallic strips 120 and 122 is affixedto attachment section 118 of carrier 104. As used herein, the bimetallicstrips 120 and 122 are arranged such that the metal with the highercoefficient of expansion comprises the inner strips.

The temperature sensor 100 of the present invention will cause relativemovement of reflective surface 112 with respect to the end of thefiberoptics 16. As temperature sensor 100 is exposed to heat, bimetallicstrips 120 and 122 will bow inward. This is caused by the fact that theinner strips 124 will expand while the outer strips 126 resistexpansion. The bowing of strips 120 and 122 will cause carrier 104 tomove farther away from the optical fiber 16 within connector section110. As carrier 104 moves farther away from the end of the opticalfiber, less light is reflected back into the optical fiber fromreflective surface 112. In this manner, temperature can be measured bythe change in reflectance of light back into the optical fiber 16.

In operation, the present invention, in its embodiments, offers ananalog measurement of environmental factors affecting either thepressure sensor 60 or the temperature sensor 100 of the presentinvention. Light source 12 of the present invention is a stabilizedlight source. This means that light-emitting diode 32 will emit atemperature stabilized, constant light output into fiberoptics 16. Whenthe reflective surface of the pressure or temperature sensors is near tothe end of the optical fiber, a large amount of this light is reflectedback into the end of the optical fiber. This light will exert a certainamount of power onto photodetector 42. As described herein previously,photodetector 42 will transmit a current signal to the transconductanceamplifier 44. Transconductance amplifier 44 will create a voltage thatis a function of the power of light hitting photodetector 42. As thelight passes to the RMS to DC converter, it is changed to a DC signalproportional to the power of light striking the photodetector 42. Thissignal, through proper adjustments of gain and offset, can be read outas an indication of either pressure or temperature affecting sensor 14.

As the reflective surface is moved farther and farther away from the endof the optical fiber, less light is reflected back into the opticalfiber and less light affects photodetector 42. As such, the signal willbe in proportion to the amount of light striking the photodetector andthus, proportional to the amount of change of either temperature orpressure acting on sensor 14. In this manner, an accurate analogmeasurement of either temperature or pressure can be accomplished by theelectronics of the present invention.

It should be noted herein that the main problem with fiberoptic sensorsis temperature stability. Through the complicated arrangement ofelements associated with light source 12, the current to thelight-emitting diode is stabilized with respect to temperature. As aresult, the light emitted by the light-emitting diode is also stable.Since a precision, stabilized light source is present in the presentinvention, the photodetector and associated electronics can present anaccurate analog measurement of environmental factors affecting sensor14. The RMS to DC converter 48 offers greater efficiency, greaterlinearity, a controllable speed, and a true conversion of power notfound hereinbefore in the prior art of temperature and pressure sensingfiberoptics. Since alternating current is difficult to work with inproducing an analog output, the conversion to DC greatly facilitatesthis analog measurement.

The output circuitry of the present invention affords the user of thepresent invention the ability to adjust gain and offset. Thus, theinstrumentation of the present invention can be adapted to varyingtemperature levels, pressure levels, or other factors affecting thesensor. The output can be further coupled to instruments that canprovide a humanly perceivable readout of the temperature and pressureaffecting the sensor. Additionally, this output could be interconnectedwith a computer for providing a control on the system being monitoredand observed.

By employing fiberoptics to the measurement of temperature and pressure,the present invention offers an inherently safe method of suchmeasurement. Since the electrical components of the present inventionare far removed from the hazardous environment or otherwise explosiveenvironment be sensed, there is no possibility that short circuits orother electrical malfunctions could create an explosion. Additionally,the sensor system of the present invention could be incorporated intoareas that have strong electromagnetic interference or areas that arestrongly susceptible to such electromagnetic interference. Since thesensor 14 is a totally passive device, and since no electricity passesthrough the optical fiber, the present invention is particularly usefulin such application.

The use of the beamsplitter-type coupler is very important andadvantageous to the present invention. This optical coupler permits asingle optical pathway to be used for the transmission of lightinformation to and from the temperature/pressure sensor. This eliminatesthe problems inherent in the complicated bundle-type arrangements ofoptical fibers, as used in the prior art. The single optical fiber canbe incorporated simply and easily within the temperature/pressuresensor. Since the integrity of only one fiber must be maintained, thefailure rates are reduced and repair is minimized. In addition, thesingle fiber arrangement reduces the cost of the optical fibers withinthe system. These are but a few of the many advantages that are achievedthrough the single fiber-beamsplitter arrangement of the presentinvention.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and various changes in the size,shape, and materials, as well as in the details of the illustratedconstruction, may be made within the scope of the appended claimswithout departing from the spirit of the invention. This inventionshould only be limited by the appended claims and their legalequivalents.

We claim:
 1. A fiberoptic sensing system comprising:a light sourcemeans; temperature sensor means responsive to an external stimulus, saidtemperature sensor means comprising:a housing; a carrier arranged withinsaid housing, said carrier having a reflective surface thereto; and atemperature-sensitive member connected to said carrier at one end andanchored to said housing at the other end, said temperature-sensitivemember causing said carrier to move within said housing responsive tochanges in temperature affecting said temperature-sensitive member, saidtemperaturesensitive member comprising:a first bimetallic strip havingan inner metallic portion and an outer metallic portion, and a secondbimetallic strip having an inner metallic portion and an outer metallicportion, said first and second bimetallic strips arranged in planeparallel to each other within said housing, said inner metallic portionsof said first and second bimetallic strips having a higher coefficientof thermal expansion than said outer metallic portions of said first andsecond bimetallic strips; fiberoptic means for transmitting light fromsaid light source means to said temperature sensor means, saidreflective surface for reflecting light from said fiberoptic means backinto said fiberoptic means, said temperature-sensitive member causingsaid carrier to change in distance between said fiberoptic means andsaid reflective surface in a direction perpendicular to said reflectivesurface; detector means arranged so as to receive the light reflected bysaid reflective surface of said temperature sensor means through saidfiberoptic means, said detector means being responsive to the intensityof light from said fiberoptic means; and output means electricallyconnected to said detector means for producing a signal relative to thelight as received by said detector means,
 2. The apparatus of claim 1,said light source means comprising:a light-emitting diode; and currentstabilizing means electrically connected to a source of electricalenergy and to said light-emitting diode for stabilizing current to saidlight-emitting diode.
 3. The apparatus of claim 2, said currentstabilizing means comprising:a Zener diode circuit; an operationalamplifier electrically connected to said Zener diode circuit; and apotentiometer electrically associated with said Zener diode circuit andsaid operational amplifier and said light-emitting diode, saidpotentiometer for setting the power level to said light-emitting diode.4. The apparatus of claim 1, said temperature sensor means furthercomprising:fiberoptic connection means attached to one end of saidhousing, said fiberoptic connection means arranged such that thelongitudinal axis of the end of said fiberoptic means passingtherethrough is positioned in perpendicular relationship to saidreflective surface.
 5. The apparatus of claim 1, said fiberoptic meanscomprising a single optical fiber from said light source means to saidsensor means.
 6. The apparatus of claim 1, further comprisingbeamsplitter means disposed about said light source means, saidfiberoptic means and said detector means, said beamsplitter means forpassing light from said light source means to said fiberoptic means andpassing said light from said fiberoptic means to said detector means. 7.The apparatus of claim 1, said detector means comprising a photodetectorpositioned relative to said fiberoptic means so as to be electricallyresponsive to light emitted by said fiberoptic means for producing acurrent relative to the intensity of the light from said fiberopticmeans.
 8. A fiberoptic temperature sensor comprising:a housing; acarrier arranged within said housing, said carrier having a reflectivesurface affixed thereto; a temperature-sensitive member connected tosaid carrier at one end and anchored to said housing at the other end,said temperature-sensitive member causing said carrier to move withinsaid housing in response to changes in temperature affecting saidtemperature-sensitive member, said temperature-sensitive membercomprising:a first bimetallic strip having an inner metallic portion andan outer metallic portion; and a second bimetallic strip having an innermetallic portion and an outer metallic portion, said first and secondbimetallic strips arranged in plane parallel to each other within saidhousing, said inner metallic portions of said first and secondbimetallic strips having a higher coefficient of thermal expansion thansaid outer metallic portions of said first and second bimetallic strips;and fiberoptic connection means attached to said housing so as to permitthe attachment of at least one optical fiber so that the end of saidoptical fiber is perpendicular to said reflective surface, saidtemperature sensitive member causing said carrier to change in distancebetween said fiberoptic connection means and said reflective surface ina direction perpendicular to said reflective surface.